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Mad cow disease

Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a fatal, neurodegenerative disease of cattle, which infects by a mechanism that shocked biologists on its discovery in late 20th century and appears transmissible to humans. While never having killed cattle on a scale comparable to other dreaded livestock diseases, such as foot and mouth and rinderpest, BSE has attracted wide attention because people assume humans can contract the disease, but it has never been proven that BSE has any link to variant Creutzfeld-Jakob disease (vCJD), sometimes called new variant Creutzfeld-Jakob disease (nvCJD), a human brain-wasting disease. more...

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Infectious agent

Unlike other kinds of infectious disease which are spread by microbes, the infectious agent in BSE is a specific type of protein. Misshapen ("misfolded") prion proteins carry the disease between individuals and cause deterioration of the brain. BSE is a type of transmissible spongiform encephalopathy (TSE). TSEs can arise in animals that carry a rare mutant prion allele, which expresses prions that contort by themselves into the disease-causing shape. Most TSEs, however, occur sporadically in animals that do not have a prion protein mutation. Transmission can occur when healthy animals consume tainted tissues from others with the disease. In the brain these proteins cause native cellular prion protein to deform into the infectious state which then goes on to deform further prion protein in an exponential cascade. These aggregate to form dense plaque fibers, which lead to the microscopic appearance of "holes" in the brain, degeneration of physical and mental abilities and ultimately death.

The BSE epidemic in British cattle

The British BSE epidemic in cattle was recognised in 1986. It was first believed to have originated in sheep, in which the related prion disease scrapie is common (such diseases collectively are called "transmissible spongiform encephalopathies" or TSEs). However, sheep and cattle TSEs are quite different and it is now thought more likely that BSE could have originated with a case of sporadic BSE in a single bovine. Prior to the BSE epidemic, cattle were fed with meat and bone meal, a high-protein substance obtained from the remnants of butchered animals, including cows and sheep. This practice allowed the accumulation of prions over many generations. As more animals became ill, more infectious tissue got into the feed, and so the number of cases reached epidemic proportions. The tissues that contain most of the pathogenic molecules are those of the brain and the nervous system, although infectious amounts have been shown experimentally to be present elsewhere, such as in blood.

The use of meat and bone meal as a protein supplement in cattle feed was widespread in Europe prior to about 1987. Soybean meal is the primary plant-based protein supplement fed to cattle. However, soybeans do not grow well in Europe, so cattle raisers throughout Europe turned to the less expensive animal byproduct feeds as an alternative. A change to the rendering process in the early 1980s may have resulted in a large increase of the infectious agents in the cattle feed. A contributing factor seems to have been lax British laws that did not require a high temperature sterilization of the protein meal. While other European countries like Germany required said animal byproducts to undergo a high temperature steam boiling process, this requirement had been eased in Britain as a measure to keep prices competitive.

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FAO says better controls and surveillance needed to protect consumers from BSE. - Food and Agriculture Organization - Bovine Spongiform Encephalopathy
From Food & Drink Weekly, 1/19/04

Controls against mad cow disease are too lax in many countries and there is a "considerable risk" of a spread of the disease, says the UN Food and Agriculture Organization (FAO). After the discovery last month of the first case of BSE in the United States, FAO urged all countries to keep risky animals and materials out of the food chain. "To reassure consumers ... will require better controls and more surveillance and testing," the Rome-based agency said. "In many countries BSE controls are still not sufficient and many countries are not applying the recommended measures properly," said FAO in a statement. "There is also a considerable risk of further introducing infectious materials, given the global trade in animal feed and animal products."

FAO is urging governments to minimize risks by applying precautionary measures that include a ban on feeding meat and bone meal to farm animals as well as stricter surveillance and identification of the cattle population. "If the control measures ... are in place and implemented effectively, the risks of infective material in the food chain are very low, even in countries where the disease is present," FAO said. Additional BSE tests would help boost consumer confidence and should be carried out on all animals that have died or are killed other than by routine slaughter, FAO said.

Here in the United States, USDA says it probably will license the first rapid BSE test in a matter of weeks and that it soon would begin accepting applications from companies that manufacture speedy BSE test kits. Test kits will be checked at USDA's Center for Veterinary Biologics to ensure that they are effective before the department issues any licenses for the product.

In addition, USDA indicated that it will shift some of the testing that traditionally was done at slaughter plants to rendering plants, and perhaps to other locations. For example, officials say, future testing could take place at plants that might currently be processing carcasses for uses other than for human consumption.

In a related action, Agriculture Secretary Ann Veneman will meet the agriculture ministers of Mexico and Canada this week for talks expected to include BSE regulations. Under Secretary Bill Hawks told reporters the planned meeting would be an opportunity for newly appointed Canadian farm minister Bob Speller to get acquainted with his North American counterparts. Hawks also said the U.S. beef industry had asked that shipments of meat that have been in limbo since Dec. 23 be tested for specified risk material as a way of assuring buyers the meat is free of BSE.

Meanwhile, GAO officials will meet later this month with senators to agree on a framework and timeline for a GAO probe into FDA's enforcement of its animal feed rules. GAO plans to brief Sens. Tom Harkin (D-Iowa), Thad Cochran (R-Miss.) and Dick Durbin (D-Ill.) on a tentative scope and design for the GAO inquiry into how FDA is monitoring and enforcing compliance with the feed rule.

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